The term "building" as used throughout this application is intended to include any structure such as an aircraft, boat or other moveable and non-moveable conventional structures.
It is well known that within buildings at night or especially when the power has been lost, it is difficult to find ones way along the necessary corridors to the building exits. Similarly, in some emergencies, the location of important fixtures such as fire alarms, extinguishers, shut-off valves and the like are difficult to find.
In the prior art, a photoluminescent material is utilized as a guide for such purposes. The luminous material is attached to doorways, hallways, and the like, so that in the event of a power outage, the photoluminescent material will glow in the dark and guide a person to an exit or along a prescribed path. Of course, it is only useful to those individuals in the building that have adjusted their eyes to the darkness. Further; the luminescence produced is significantly lost within the first 20 minutes of an "outage." This makes it virtually useless to anyone entering the building after a short period of time.
The present invention overcomes the disadvantages of the prior art by providing a single sheeting material having both photoluminescent and retroreflective properties. The sheeting should exhibit the same photoluminescent properties as the current product being used, and it has significant retroreflective properties.
Thus it is an important object of the present invention to provide a photoluminescent retroreflective sheet material that is designed to provide both photoluminescence and retroreflection of light.
It is also an object of the present invention to provide a photoluminescent retroreflective sheeting in which a phosphorescent pigment is added to the retroreflective layer.
It is a further object of the present invention to provide a photoluminescent retroreflective sheet in which the retroreflective layer has cube corner retroreflectors embossed on the backside thereof and covered by a predetermined pattern of hydrophobic silica. A backcoating contains the phosphorescent pigment and is in contact with the retroreflective layer in areas of the pattern not covered by the hydrophobic silica.
It is yet another object of the present invention to provide a photoluminescent reflective sheet which has a transparent flexible film with retroreflective cube corners formed on the reverse surface thereof and a clear adhesive with phosphorescent pigment screen-printed in a pattern and cured on the cube corners.
It is believed that the present invention may be utilized with retroreflector sheeting produced in a variety of ways but will be particularly useful with that retroreflective sheeting described and claimed in U.S. Pat. No. 4,618,518, issued Oct. 21, 1986, to Robert M. Pricone, et al. and assigned to applicants' assignee, the disclosure of which is incorporated by reference. Other forms and methods of producing retroreflective sheeting include those of "casting" cube corner elements, such as disclosed in Rowland U.S. Pat. Nos. 3,810,804, issued May 14, 1974; 3,684,348, issued Aug. 15, 1972; and 3,689,346, issued Sep. 15, 1972.
Useful apparatus for embossing a film to provide cube corner retroreflective elements is disclosed in Pricone, et al. U.S. Pat. No. 4,601,861, issued Jul. 22, 1986, commonly assigned. Other techniques for compression or sequential embossing are disclosed in Rowland U.S. Pat. No. 4,244,683, dated Jan. 13, 1981.
Efforts have been made in the past to utilize fluorescent pigmented materials in conjunction with retroreflective sheet materials of the cube corner type. However, such use of fluorescent materials was intended to provide a combination of day/night visibility in highway signs. One example is that found in Rowland U.S. Pat. No. 3,830,682, issued Aug. 20, 1974. However, in such uses, unlike phosphors, the flourescent material would not continue to glow or provide light under "darkened" conditions but instead is illuminated by the light of certain wave lengths, so as to provide some "daylight" visibility to highway signs.
The present invention utilizes a phosphorescent pigmentation in conjunction with retroreflective sheet material in a manner which does not materially impede the retroreflective capability of the sign when illuminated either under normal lighting conditions, such as in a building and under hallway lighting lights, nor does it impede the "dark" or night light retroreflective capability when illuminated by a flashlight or other temporary light source.